Introduction
The sounds in our environment carry a great deal of information. The sense of hearing in most mammals is highly developed to allow them to extract useful information from sound and humans are no exception. We are constantly monitoring the noisy environment we live in, extracting information we need or want from it and discarding the rest.
We can also analyze sounds mathematically to extract very detailed information about the sources of sound. In the following examples we will analyze sounds using a free software program called Raven Lite. Raven Lite is a very user friendly program written by the folks at the Cornell Bioacoustics Laboratory that allows the user to record sounds, to save them in a variety of formats, and to analyze both the frequency and temporal components of sound.
The reason for Raven Lite’s existence is to record and analyze the vocalizations of birds and insects but it can be used to explore other aspects of sound as well. Some of those other things are what I will describe here. The software is limited in some of its capabilities but is a great tool for exploring sound.
So download, register, and install the software and give it a try. Here is where you go to get it……. http://www.birds.cornell.edu/brp/raven/RavenOverview.html
Overview of Raven Lite
This is not meant to be a Raven Lite Tutorial. Rather it is a very brief overview of its features and capabilities. Most of the action takes place in the File menu and on the large tool bar above the waveform and spectrogram display. The File menu is used to choose sound files to load and analyze or to record new sounds into memory or to disk. The default display is the waveform and spectrogram shown one above the other.
The large tool bar allows the user to change the display parameters for improved contrast and different color palettes, and to playback the recorded sound while watching the display.
Four Projects:
Subsequent pages will describe four basic projects that can be done using Raven Lite as the analysis tool. They are not meant to be complete. Once you start playing around with it lots of possibilities come to mind.
The projects are:
1. Estimate the speed of sound in air.
2. Analyze the sound of a machine to learn about its operation.
3. Estimate the speed of a car or truck using the Doppler shift of a sound source on the vehicle.
4. A more advanced Doppler shift analysis of a Chinook twin rotor helicopter passing overhead in which we extract some operating information from the sound.
5. Another Doppler shift analysis of an AirTractor AT-502B agricultural aircraft using techniques similar to the Chinook helicopter analysis.
Murmurs from the Earth... 